In accordance with the ever-increasing growth in wireless and wire-line communication markets, it is desirable that integrated circuits, such as analog and RF front-ends, operate with wider bandwidths in higher frequency ranges, such as the multi-Gigahertz range. One circuit architecture capable of performing at such a level is the distributed amplifier circuit architecture. A distributed amplifier typically trades delay with bandwidth in order to achieve a much higher bandwidth than a lumped architecture. There have been tremendous efforts to use and implement distributed architectures in various technologies within the communications and other markets.
Distributed amplifiers generally employ a topology in which inductors or transmission lines (T-lines) separate two or more uniform amplifier stages, yet the output currents from each individual stage can combine in an additive fashion. Viewed from another perspective, the parasitic capacitances of the various amplifier stages are absorbed into the actual (or artificial) transmission lines resulting in a higher bandwidth. However, despite the additive nature of the gain, the distributed architecture still produces a relatively low overall gain and gain-bandwidth product.
One of primary sources of performance degradation in distributed amplifiers is the non-zero inductive loss and non-zero output resistance of the amplifier stages, which can decrease both the overall gain and bandwidth. The inductive loss typically increases with frequency due to the skin effect phenomenon. As a consequence, the bandwidth of the distributed amplifiers is generally dependent on the amount of loss in the transmission lines.
Thus, improved systems and circuits are needed capable of operating in higher frequency ranges with improved gain-bandwidth products.